This invention concerns method and means for fastening in porous materials as for instance cell plastic. (The term porous materials is here meant in a broad sense, covering also granulous and other easily penetratable materials.) Cell plastic materials as well as other porous materials have very good heat insulating properties and they have therefore been more and more used in the building technique. Pure sandwich constructions with a core of polyurethane cell plastic between two metal sheets are of great importance in connection with industry buildings. Constructions of this type, below called panels, have in particular with great success been used all over the world for freezing chambers, cold-storage rooms and cold-storage warehouses in the two latest decades.
Mostly the panels are provided with groove and tenon and appropriate seals. In buildings for freeze storage an unyieldable requirement is that the joint between the panels is sealed against diffusion. This is achieved by locking the panels together with a locking device giving a permanent compression of the sealing strips and thus a permanent sealing function.
The locking device usually comprises of two halves that have been placed centrically in the cell plastic core close to the edges of the panel. The placing demands great accuracy in order to secure on mounting that the lockhalves in adjacent panels have exactly coinciding positions. A small deviation means a loss of the locking possibility and presumably a discarding of that panel.
The panels are fabricated according to one method in rigid moulds or jigs, where surface material and locks are firmly held in their positions before the interior of the panels are filled by foam by the injection of chemicals. According to a second method, the panels are fabricated in a continuous process where all parts are fed through a double band press at the foaming process. In a third process each panel is glued together of metal and foam sheets.
A correct fastening or enclosure by foam of parts as for instance locks, is a troublesome and costly operation, in particular in continuous fabrication. Instead of directly fastening parts by surrounding them by foam, these can afterwards be mounted in the finished panel. A cavity is machined in the cell plastic core, the part is placed in the cavity and is foamed or glued in place.
The shape and construction of the locking halves varies, but the main principal for fastening in the foam is rigid load taking lateral flanges. When mounting panels it is connected with great difficulties to change the position of faulty lock halves or to mount additional locks.
A further possible fastening would of course be to use expanding bolts of known type, but these will, to start with, not give a very good grip and secondly the expansion might easily deform the panels.